Question

It’s possible to create lots of memory-intensive objects and then abandon references to them. For example, I might want to download and operate on some data from a database, and I will do 100 separate download and processing iterations. I could declare a DataTable variable once, and for each query reset it to a new DataTable object using a constructor, abondoning the old DataTable object in memory.

The DataTable class has easy built-in ways to release the memory it uses, including Rows.Clear() and .Dispose(). So I could do this at the end of every iteration before setting the variable to a new DataTable object. OR I could forget about it and just let the CLR garbage collector do this for me. The garbage collector seems to be pretty effective so the end result should be the same either way. Is it “better” to explicitly dispose of memory-heavy objects when you don’t need them, (but add code to do this) or just depend on the garbage collector to do all the work for you (you are at the mercy of the GC algorithm, but your code is smaller)?

Upon request, here is code illustrating the recycled DataTable variable example:

    // queryList is list of 100 SELECT queries generated somewhere else.
    // Each of them returns a million rows with 10 columns.
    List<string> queryList = GetQueries(@"\\someserver\bunch-o-queries.txt");
    DataTable workingTable;

    using (OdbcConnection con = new OdbcConnection("a connection string")) {
        using (OdbcDataAdapter adpt = new OdbcDataAdapter("", con)) {
            foreach (string sql in queryList) {
                workingTable = new DataTable();  // A new table is created. Previous one is abandoned
                adpt.SelectCommand.CommandText = sql;
                adpt.Fill(workingTable);
                CalcRankingInfo(workingTable);
                PushResultsToAnotherDatabase(workingTable);
                // Here I could call workingTable.Dispose() or workingTable.Rows.Clear()
                // or I could do nothing and hope the garbage collector cleans up my
                // enormous DataTable automatically.
            }   
        }
    }

Answer 1

Ok, time to clear things up a bit (since my original post was a little muddy).

IDisposable has nothing to do with Memory Management. IDisposable allows an object to clean up any native resources it might be holding on to. If an object implements IDisposable, you should be sure to either use a using block or call Dispose() when you’re finished with it.

As for defining memory-intensive objects and then losing the references to them, that’s how the Garbage Collector works. It’s a good thing. Let it happen and let the Garbage Collector do its job.

…so, to answer your question, No. It is not a bad practice to depend on the .NET Garbage Collector. Quite the opposite in fact.